The present invention relates to a semiconductor integrated circuit and further relates to techniques to facilitate debugging or device tests on individual signals interchanged between functional modules contained in the semiconductor integrated circuit. For example, it relates to a technique which is effectively applied to a microcomputer constituted in an application specific system.
Many functional modules are mounted on a semiconductor integrated circuit such as a single-chip microcomputer which is constituted with a plurality of functional modules on a semiconductor substrate. The modules mounted are, for example as shown in FIG. 4, a CPU (central processing unit) 1, a DMA (direct-memory-access) controller 2, a timer 3, a serial interface controller (not shown in the drawing) and other peripheral circuits. These functional modules are connected to an internal bus 4 which includes an address bus, a data bus and a control bus. Common signals such as data, address signals or control signals can be interchanged among functional modules and especially between the CPU and the modules. Signals necessary for the operation of these functional modules are not only the above-mentioned common signals, there also are some individual signals which have to be interchanged individually between specified modules. Following are examples of these signals: a DMA request signal DREQ by the DMA controller 2 requesting CPU 1 to open the common internal bus 4, a DMA acknowledgment signal DACK which is a response signal to a DMA request, an interruption signal INT2 or INT3 for specifying an interruption to be given to the CPU 1 by the DMA controller 2 or the timer 3. It has been considered that these individual signals are exclusively used for the handshake control between the specified functional modules, so that the individual signals are not open to the outside and also there is no need to be open to the outside, while the internal bus 4, forming a contrast with the above signals, is arranged to be capable of being interfaced with the outside through an input/output circuit 5.
In the device test of a semiconductor integrated circuit such as a single-chip microcomputer where individual signals are interchanged among built-in functional modules, concerning common signals, a signal can be supplied to a desired functional module from the outside through the internal bus 4 and the module can be tested being independently controlled. But in the case of an individual signal which such as an interruption signal is not open to the outside, it is impossible to supply the signal from outside or to confirm the outputting condition of the signal from outside. In a test of individual signals therefore, it is necessary to operate both functional modules simultaneously; between them a specified individual signal is interchanged. According to the investigation made by the present inventors, to confirm the outputting condition of a specified individual signal and the operating condition of a functional module which is to receive the individual signal, it is necessary to make the functional module, which is to output the individual signal, perform an operation necessary to obtain the desired outputting condition of the signal, and to make the functional module to receive the signal perform an operation which is capable of reflecting the condition of the individual signal. Therefore, the points to be discussed are the a long time needed for the test on individual signals and also for making test patterns.
In a semiconductor integrated circuit device which has a plurality of built-in logical functional blocks, the documents on the technique to take out an individual signal to be used among the above-mentioned logical functional blocks to the outside of the semiconductor integrated circuit device and to supply a test signal input from outside the semiconductor integrated circuit device to a specified logical functional block, are listed as shown below.
U.S. patent application of Ser. No. 199,605, now U.S. Pat. No. 4,967,387. PA1 Japanese Patent Application laid open on Feb. 2, 1987 under Provisional Publication No. 38949/87 PA1 Japanese Patent Application laid open on Dec. 2, 1986 under Provisional Publication No. 272668/86
The semiconductor integrated circuits described in the above patent application documents are provided with exclusive use signal lines added for tests.